245/275

[The Radium King]

hi. looking to go wider front and back on my car. 18" wheels. currently running:

235/40 (10mm wider in front) and 265/35 rear (OEM).

pretty content with the balance this gives the car. I want more front tire, so thinking I should widen the rear also. I realise there are pros/cons to this, and hope to report back on any changes I experience with this setup (ie, diameter impact on gearing and torque, impact on power given need to turn bigger rubber, any changes to front/rear balance, etc.).

I am thinking the following:

245/35 and 275/30

concerns are fit, diameter vs OEM, and diameter variation front/rear (so as not to mess w abs). here's my analysis of diameters:

225/40 (25.1) 265/35 (25.3) OEM
235/40 (25.4) 265/35 (25.3) current
235/35 (24.5) 265/35 (25.3) 3.3%
235/35 (24.5) 265/30 (24.3)
-
245/35 (24.8) 275/30 (24.5) proposed
245/35 (24.8) 275/35 (25.6) 3.2%
245/40 (25.7) 275/35 (25.6) confirm front fit

the proposed size reduces diameter front and rear, keeps front/rear diameters within tolerance, and should fit (front w spacers - ET53 and 7 mm spacer).

anyone have any experience with these widths that they could share? am I on track w sidewall heights? thanks.

[steved0x]

Originally Posted by The Radium King

245/40 (25.7) 275/35 (25.6) confirm front fit

I don't have any feedback on the other ones, but this size won't fit in the front if you have the OEM struts up front - the tire will hit the lower spring perch (or whatever it is called... ) I don't know about the back but I did fit a pair of 285/35/18 on the back, and although it looked successful I never drove on it because the fronts I had to go with it didn't fit (got them from a Cayman guy)

I have seen folks run this size successfully with PSS9 however since they don't have that big lower spring perch.

[j.fro]

I ran 245/40/18 NT01 tires on the front & 275/35/18 NT01 on the rear with 18x8 18x10 Carrera Lightweight reproductions for a few years. On the front I used 7mm spacers, 14 on the rear. This combo was lighter than my stock 18" turbo twists with inexpensive all season tires and acceleration was noticeably quicker. The nittos rubbed a bit at full lock in both directions, but that didn't bother me. The car NEVER had any understeer. Turn in was spot on. As the rears wore, or on cold days, I would get oversteer. I removed the rear sway bar and it cleaned this up very nicely.
Last year I switched to Hoosier A7 245/35/18 and 275/35/18. The rears are pretty much the same dimensions as the Nittos. The fronts are waaaay off. They are at least an inch wider, if not more. the tire is cantilevered on the rim and really should be on an 8.5 or 9". They react to both temp and tire pressure very differently, and I chased a horrible understeer problem all year. I couldn't get the rears to brake free no matter how hard I tried. It was a rough year.
I'm on coilovers, so I can't comment on how the diameter affects rub on the spring perch.

[The Radium King]

thanks lots. so, my understanding is that a smaller overall wheel/tire diameter will increase torque but reduce top end. on the rear you went from an OEM 265/35 to 275/35 which in an increase in diameter (25.3 to 25.6 or +.3"). however you noticed an increase in acceleration so one can assume that the increase in diameter was more than offset by the reduction in rotational mass (lighter wheels and tires)?

odd on the hoosiers. must be cheater tires (if you have the right rim width) - do you think you were rolling onto your sidewall?

[j.fro]

Yeah, on the rears the bigger wheels/tires were about 5lbs lighter each. The fronts were about 3lbs lighter each.
When the Hoosier A7 tires came out, replacing the A6, there were a number of sizes that seemed way off from their predecessors. SCCA boards were lit up all over the place.

[BYprodriver]

Originally Posted by The Radium King

thanks lots. so, my understanding is that a smaller overall wheel/tire diameter will increase torque but reduce top end. on the rear you went from an OEM 265/35 to 275/35 which in an increase in diameter (25.3 to 25.6 or +.3"). however you noticed an increase in acceleration so one can assume that the increase in diameter was more than offset by the reduction in rotational mass (lighter wheels and tires)?

odd on the hoosiers. must be cheater tires (if you have the right rim width) - do you think you were rolling onto your sidewall?

Don't forget spacers weight. I don't believe there is any way to increase acceleration by installing taller tires on a Boxster unless you are testing 0-60 & don't mind sacrificing a clutch. I've never seen a 275/30/18 tire.

[The Radium King]

Originally Posted by BYprodriver

Don't forget spacers weight. I don't believe there is any way to increase acceleration by installing taller tires on a Boxster unless you are testing 0-60 & don't mind sacrificing a clutch. I've never seen a 275/30/18 tire.

holy trump, you're right. no 275/30, and a 275/35 is bigger diameter than a 265. what to do? 285/30 fit ok? that's a lot of rear tire. perhaps stuck with a 265 in the back.

[The Radium King]

so, after some sober review of what is actually available in tire sizing, and with the intent to not increase the rear tire diameter, I am here:

OEM:

225/40 (25.1) 265/35 (25.3)


Current (upsized fronts):

235/40 (25.4) 265/35 (25.3)


options:

245/40 (25.7) 265/35 (25.3) Even wider fronts - too much front tire?

245/40 (25.7) 275/35 (25.6) Wider fronts and backs, but can't get a 275 in a smaller sidewall so would see higher gearing.

255/35 (25.0) 285/30 (24.7) Super wide, smaller diameter - but will they fit?!?!?!?

so, anyone with experience running a 245/265 combo? anyone with experience fitting a 255/285 combo? i'm on coilovers, so hopefully no perch interference issues.

[BYprodriver]

Originally Posted by The Radium King

holy trump, you're right. no 275/30, and a 275/35 is bigger diameter than a 265. what to do? 285/30 fit ok? that's a lot of rear tire. perhaps stuck with a 265 in the back.

285/30/18 fit ok with proper wheel offset & give very noticeable acceleration improvement with stock 3.2L. However additional weight & treadwidth make the car less nimble which is why I just sold 2 pair of 10" Carrera II wheels. I say run the best 265 tire for your application.

[lkchris]

In the real world, here's what you'll accomplish fitting larger than oem tires:

You'll make the tire company happy because they've sold you a more expensive tire.

You'll have increased your car's unsprung weight, affecting handling and fuel mileage.

You'll have increased your car's rolling resistance, affecting fuel mileage.

You'll have decreased your car's traction capabilities on wet or snowy roads.

[Racer Boy]

Generally speaking, you want to avoid taller gearing (what taller tires will give you). Do you run at any tracks where you reach top speed? If you do reach the car's top speed, is it because you are on the rev-limiter? If not, then you'll gain more from the shorter gearing giving you quicker acceleration.

[heliguy]

I run 275/35/18 in the rear of mine on the stock Carrera Lights and they work just fine with spacers. No problems with the slightly taller profile. The height difference (92.75mm) vs (96.25mm) is only 3.5mm and is so negligible it wasn't a concern for me.

[anotherturbo]

As for fitment...I run 255/35/18 in the front and have the slightest rubbing at full lock, and 295/30/18 in the rear with no clearance issues. I do however have coilovers and rolled fenders.

[The Radium King]

bah, humbug. toyo canada has no 255, 275 or 285 in stock. looks like I am forced to be prudent and get a 245F/265R setup or pay heinous exchange rates.